Methods For Producing Sodium Hypochlorite With a Three-Compartment Apparatus Containing an Acidic Anolyte

Abstract

An electrochemical method for the production of a chlorine-based oxidant product, such as sodium hypochlorite, is disclosed. The method may potentially be used to produce sodium hypochlorite from sea water or low purity un-softened or NaCl-based salt solutions. The method utilizes alkali cation-conductive ceramic membranes, such as membranes based on NaSICON-type materials, and organic polymer membranes in electrochemical cells to produce sodium hypochlorite. Generally, the electrochemical cell includes three compartments and the first compartment contains an anolyte having an acidic pH.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of U.S. Provisional Application No. 61 / 091,627, filed Aug. 25, 2008, entitled “Three Compartment Apparatus and Method for Producing Sodium Hypochlorite” and U.S. Provisional Application No. 61 / 120,737, filed Dec. 5, 2008, entitled “Three Compartment Electrochemical Process for Production of Sodium Hypochlorite,” the entire disclosures of which are hereby incorporated by reference.FIELD OF THE INVENTION[0002]The present invention relates in general to electrochemical processes for the production of a chlorine-based oxidant product. More particularly, the present invention provides an electrochemical method for producing one or more chlorine-based oxidants, such as sodium hypochlorite and hypochlorous acid, through the use of a multi-compartment, electrolytic cell that includes an anion-conductive membrane, an alkali cation-conductive membrane, and an anolyte having an acidic pH.BACKGROUND OF THE INVENTIO...

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Benefits of technology

[0010]The pH and concentration of the feed stream or streams added to the compartments can be controlled so the fluid in each compartment has a pH that allows the cell to function as intended. In other words, the fluids in the 3 compartments can be tailored to have any suitable pH. That said, the anolyte in the first compartment may have a pH that is less than about 7, and in some instances, less than about 4. This acidic pH of the anolyte may increase the amount of chlorine gas and hypochlorous acid and other chlorine-based oxidants that are generated at the anode during cell use.

[0012]The acidic pH will also prevent precipitation of water insoluble salts of calcium, magnesium on the anionic and cationic membranes. This will increase the longevity of electrolytic cell operation when used with salt water sources such as sea water, R.O. brine water and tap water.

[0016]In this second example, a final feed stream comprising water, an aqueous sodium chloride solution sodium chloride, and / or an aqueous solution of sodium hydroxide is added as a catholyte to the third compartment, where sodium hydroxide is produced. In some cases, the catholyte is then continuously re-circulated through the third compartment, causing the concentration of sodium hydroxide in that compartment to increase.

Problems solved by technology

While the above-mentioned production methods are used to create large amounts of sodium hypochlorite, such methods are not without their shortcomings.

In one example, some methods for producing sodium hypochlorite are inefficient and expensive.

For instance, some methods require relatively large amounts of electricity to be spent for each unit of sodium hypochlorite that is produced.

In another example, certain conventional production processes are essentially immobile and thus prevent sodium hypochlorite, which has a limited shelf life, from being produced at the site where it is to be used.

In another example, some conventional methods expose components of an electrolytic cell, namely the cathode and anode, to relatively harsh conditions (e.g., scaling and degradation), which tend to shorten the components' operational lifespan.

In a final example, some methods are not able to produce sodium hypochlorite at a near-neutral pH, which may easier to handle than extremely acidic or basic forms of the oxidant.

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